Drafting instrument



March 28, 1944.

M. R. HULL DRAFTING INSTRUMENT Filed' Nov. 4, 1941 F/G. '5 INVENTOR777mm $1M.

Patented Mar. 28, 1944 UNITED I STATES PATENT OFFICE DRAFTING INSTRUMENTMonroe R. Hull, Anaconda, Mont.

Application November 4, 1941, Serial No. 417,797

1 Claim. (01.33-75) V I For, generations the conventional draftingtools, used whe drawing straight lines, have been a T square or parallelruler for drawing horizontal lines, a 45 triangle, a 30 x 60 triangleand a protractor for use in drawing lines at angles other than 30, 45and 60.

The instrument .I have invented is to be used in conjunction with aconventional T square or parallel ruler and is a combination of amodified 45 triangle, a modified 30 X 69 triangle and a protractor.

An object of this invention is to provide, at low cost, an instrumentthat will enable a draftsman to do accurate work more rapidly than canbe done with separate triangles and protractor.

Another object is to provide a time saving instrument, precise inconstruction, pleasing in appearance, strong and durable and wellbalanced, having a protractor that may be:

quickly set and firmly locked in position.

A further object is to provide an instrument having one edge that may beset at any desired angle and when so set, it will have other edges fordrawing lines at 30, 45, 60 and 90 and for drawing the sloping lines ofthe flanges of American standard I beams and channels.

A still further object is to provide two nonoverlapping protractorscales giving the draftsman the option of setting the instrument by ascale of degrees or of slopes in inches per foot.

A fifth object is to provide an instrument that is especially useful fordrawing symmetrical structures, such as roof trusses, towers, bevelgears, etc., since nearly all lines of such structures can be drawn atone setting of the protractor.

The construction, which makes possible the attainment of the variousobjects of this invention, is shown in the accompanying drawing inwhich:

Figure 1 shows an assembly of the instrument.

Figure 21 is a sectional view on line of Figure 1.

Figure 3 is a detail of the clamp screw.

Figure 4 is a detail of the pivot screw.

Figure 5 is a detail of a washer for the clamp screw.

Figure 6 shows the instrument in various positions relative to a Tsquare, as required to draw Figure '7.

Figure 7 and Figure 8 respectively show a roof truss and a pair of bevelgears. These are typical examples of work done with this instrument.Horizontal lines were drawn by the use of the T square. 7 All otherlines of Figure. 7. and nearly all other lines of Figure 8 were drawnwith the instrument at one setting of the. protractor for each figure. 1

' In Figure .6 the instrument, as shown in positions A and B and in thefull lines of position 10,

has the same protractor setting. In position'A side B! is parallel toline R of Figure '7. In position B side BI is perpendicular to line B.In position C (full lines) side A2.is parallel'to line L of Figure '7and side 'Al is perpendicular thereto. x f In position C '(dot dashlines) I side'Al is parallel to line R of Figure '7 and side A2 isperpendicular thereto. It is obvious that angle I equals angle 2 (Figure6, C) and that the draitsman may setside A2 parallel to line L of Figure'7 or side Al parallel to line B. 1 l

This inherent characteristic makes 'it possible to provide twoseparate'protractorscales each covering an arc of 45.

One of these scales is divided into equal spaces and marked in degreesand the other is divided into unequal spaces and marked in inches perfoot of slope as roughly indicated in Figure 1.

General description Figure 1 shows this instrument comprising twomembers, A and B, pivotally connected at O (by means to be laterdescribed) so that any required angular relation between them may beobtained. Clamping means (described later) hold A and B in the desiredangular relation and this relation is shown on the protractor scale ofB.

When parts A and B are set in the relation shown in Figure 1, they andpart C are all symmetrical, in outline, about line 2-2. Parts A and Bare so proportioned that sides Al, A2 and BI are all of equal length andare all tangent to a circle of radius R centered at 0.

Parts A and B are of thin, flat, preferably transparent, material ofequal thickness and both are made to lie fiat on the drawing board withno part of the instrument extending below their under surface.

These parts may be made of metal, but transparent or translucentmaterial is preferred: such as Celluloid or a plastic material such asVinylite. They may be fabricated from sheets or cast in molds.

For part C, metal, such as Duralumin, is preferred; however, parts A andC could be integral if cast .in a mold.

Detailed description Part A has a hole through it bounded by sides A3,A4, A and A6 and a circular arc A1, centered at 0. Sides A3 and A4 areat slopes of 1 to 6 relative to side Al and sides A5 and A6 have thesame slopes relative to side A2. are for use in drawing the slopingflanges of American standard I beams and channels. Arc A8 of part A hasa radius slightly greater than are B2 of part B. Arcs A8 and B2 areconcentric about 0.

Rigidly attached to the upper surface of part A, by countersunk head,screws I, or otherwise, is a connecting arm C which extends over part Ba sufllcient distance to receive clamp screw D, which is rigidlyattached, as described later, to

These part B. Part C is terminated by circular arcs Cl and C2 centeredat O. Arc Cl is of sumcient length to accommodate a vernier scale to beused L in conjunction vn'th the protractor scale of part B. Part Ccontains a circular slot C3, the length and width of which are such asto allow the cylindrical portion DI, of clamp screw D, to swing freelytherein through an arc of 90 about the center 0. The center line of thisslot has a radius of .375 R. (Preferably) Part C has a cylindrical bore,centered at O, to fit snugly and rotate on the cylindrical portion El ofpivot E shown in Figure 4.

Part B has two bored and counterbored holes, B3 and B4 (Figure 2)located on its center line, or line of symmetry. Hole B3, centered at O,is to receive pivot E of Figure 4 and hole B4 is to receive clamp screwD of Figure 3. The center to center distance of these holes ispreferably .375 R. The bore and counterbore B3 are to fit tightly theshank El and knurled head E2 of pivot E and the bore and counterbore B4are to fit tightly the shank DI and knurled head D2 of clamp screw D sothat D and E are firmly set into part B and cannot turn therein.

Washer F (Figure 5) is located between nut D and arm C (Figure 2) andits function is to facilitate accurate setting of the part B in itsangular relation to part A. Rotation of washer F is prevented by anintegral key Fl, in opening F2, which slides in the keyway D3 of clampscrew D. Nut H is threaded to fit the threaded portion of clamp screw Dand, when tightened, parts B and C are firmly clamped together.

Pivot E (Figure 4) has no clamping efiect, and nut G is turned relativeto E, only when assembling the instrument or taking it apart. Thecylindrical portion El is of such length as to extend through andslightly above part C, and nut G (Figure 2) is screwed tightly againstshoulder E3. Nut G, which is near the center of gravity, is grasped whenthe instrument is to be lifted or rotated.

Prior to my invention drafting instruments have been made having twomembers pivotally connected in adjustable angular relation, and,therefore, I do not claim broadly such a combination:

But, I claim:

A drafting instrument consisting of two principal triangular membershaving adjustable angular relation about a common central pivot which islocated at the center of the hypotenuse of the first member and at theapex of the second member, the first member having twolexterior straightsides of equal length at 90 toeach other and at to its line of symmetry,two interior straight sides of equal length each of which is at an angleof 30 to one of the exterior sides, the second principal member being a45 triangle the hypotenuse of which is of the same length as one of theexterior sides of the first member.

MONROE R. HULL.

